A broaching apparatus for carrying out a broaching operation has hitherto been known as described in Japanese Examined Patent Publication No. Hei 5-65287 and Japanese Unexamined Patent Publication No. Hei 6-55333.
A "circular broaching machine" described as in the former publication above employs a disk shaped tool or a broaching cutter having on its periphery a rough machining edge and a finish machining edge and adapted to be rotated relatively slowly to cut or to turn (or lathe) a rotating workpiece. With the ability to broach a workpiece on a lath, such a machine tool has an advantage of yielding a machined product that is better in quality than with a lathe or a planing machine or miller.
On the other hand, an "apparatus for the fixation of a broaching cutter" as described in the latter publication above is designed to ease an exchange of broaching tools in a broaching machine and is provided with a fit section for accepting a broaching tool and a clamp means for fixing a broach shaft to the drive shaft, on the side of a drive shaft, and a center for supporting the broach shaft rotatably, on the side of a support shaft. There, the drive shaft is adapted to be driven into rotation, by a motor for rotating the broaching cutter, via a reduction gear that couples the motor to the drive shaft.
A broaching machine as described in either of both these publications, in which a broaching tool is rotated to machine a workpiece and hence a large cutting torque acting on a drive system in machining is inherent and then requires the drive system with a reduction ratio large enough to withstand the large cutting torque. However, drive systems with a larger reduction ratio inconveniently makes the equipment larger in size and more costly.
On the other hand, the broaching tool in a finish machining operation develops less cutting torque acting on a drive system and may then have the drive system less in reduction ratio to bear the cutting torque. Also, used in a turning operation a tool to be indexed is desirably rotated rapidly in order to shorten the time of indexing and then makes the use of a drive system of less reduction ratio desirable in order to enhance the efficiency of operation.
With a conventional broaching machine as described in either of the publications mentioned above, however, there inconveniently ensues only a poor operating efficiency because of a prolonged time of indexing that inherently entails.